Gloves – a handy guide!

First published see.leeds.ac.uk on 23rd October 2015. Updated 10th Feb 2017 and 6th May 2017 by Andy Connelly.

“Seeing students doing practical chemical work in rubber gloves makes me weep. Chemistry is the science of the transformations of matter, and to practice that one needs all one’s senses, and that used to include not only sight and smell but touch (alkaline is slippery) and (discretely used) taste !”

Professor Emeritus Peter H. Plesch [1]

Introduction

Professor Plesch’s advice above gives a wonderful impression of a bygone age of chemical research when you could really get “stuck in”. This may also be the reason for the often cited, probably “post-truth”, lower life expectancy for chemists [2]! However, most of us now are unlikely to follow his advice. We actively avoid such intimate contact with chemicals by using personal protective equipment (PPE) such as the rubber gloves, or more likely nitrile, so lambasted by Professor Plesch above. The question is, are those gloves up to the job?

DISCLAIMER: I am not an expert on gloves and have no Health and Safety qualifications. The content of this blog is what I have discovered through my efforts to understand the subject. I have done my best to make the information here in as accurate as possible. If you spot any errors or admissions, or have any comments, please let me know. Do not rely on this information for your safety.

Figure 1: Author showing glove removal technique with strawberry jam.

Chemical absorption through the skin can be scarily rapid. One study showed that methyl ethyl ketone (MEK) when applied to the skin of the forearm was detected in the breath of the volunteers within 3 mins of contact [3]. From skin to lungs to mouth within 3 minutes, less if the arm was damp – that is fast. MEK is a relatively harmless chemical; however, many other chemicals can be absorbed through the skin including dichloromethane and benzene; both of which can be toxic and carcinogenic. So, we wear gloves to protect us, right?

Karen Watterhahn

karenwetterhahn
Figure 2: Karen Watterhahn

Karen Watterhahn was a Professor of Chemistry at Dartmouth College (New Hampshire, USA). While preparing a standard of dimethylmercury in a fume cupboard she spilled one or two drops onto the latex examination glove she was wearing. As she was wearing gloves and working in a fume cupboard she thought nothing of it. She finished her work, peeled off her gloves and then thoroughly washed her hands; all standard procedures. However, tests later revealed that the dimethylmercury had permeated the latex glove and within about 15 seconds had entered her skin. Five months later she was nauseous, had headaches, suffered loss of balance and finally fell into a coma. She died on June 8th 1997 of mercury poisoning at age 48. [4]

This shows that not all gloves are made equal. Assuming a glove does not fail physically (e.g. tear, pinhole, or pores) it can still fail as the chemical diffuses through the glove. In many cases the permeated material may appear unchanged to the human eye. The time taken for diffusion through the glove is known as the breakthrough time; the rate is known as the permeation rate. The breakthrough time is measured using the apparatus shown in Figure 3. This process has many variables:

  • Chemical and its concentration;
  • Glove material;
  • Thickness of the glove;
  • Temperature; and
  • Whether the glove material is being flexed.

These variables are measured under BS EN 374 [5] which states that such gloves must have a breakthrough time (or permeation time) of at least 30mins for a minimum of three chemicals from a list. However, this is only 30mins and only three chemicals, none of which might be relevant to your work.

If you want more information about the breakthrough time for a glove with a specific chemical you are using you need to approach the manufacturer. Some companies are better at providing this than others (see Table 1).

chemical_compatibility
Table 1: Example of a chemical compatibility guide for a nitrile glove. From Kimberly-Clark* Nitrile Gloves.
Glove test cell
Figure 3: Glove test cell. Glove material is placed as a membrane in the middle with test liquid on one side and a gas the other. The gas is analysed for contamination.

Choosing a glove

So, how do you choose a glove? The best place to start is by looking at the (Material) Safety Data Sheet (SDS).

Reading Safety Data Sheets

A good quality SDS will provide guidance on what glove you should use to protect yourself from the chemical in question. Others will provide less useful guidance, such as:

“Wear appropriate protective gloves and clothing to prevent skin exposure.”

The following are excerpts  from the SDS for acetone and concentrated nitric acid. They show different advice dependent on chemical.

SDS for acetone
Figure 3: SDS for acetone.
SDS for concentrated nitric acid.
Figure 4: SDS for concentrated nitric acid.

The choice of glove for acetone is particularly interesting as many lab users will wear standard (examination type) nitrile gloves while using acetone. These gloves usually have <1min breakthrough time for acetone (see Table 1). They do not protect you, if people know this—which I doubt—then they are balancing the perceived risk from acetone with the annoyance or changing gloves to something more resistant. This may be perceived as an acceptable risk with acetone but there are many chemicals where laziness, or ignorance, could be dangerous – see Karen’s story above.

Different materials

As you can see from the SDSs above there are various different materials used for gloves. Below is a list of some common materials used for laboratory gloves. The following information is for general reference only, for specific recommendations contact the glove manufacturer, consult the SDS, or talk to your local H&S officer [6]:

  • LATEX is a natural rubber that is inherently elastic and resilient. It is recommended for weak acids, weak bases, alcohols, and aqueous solutions but not oils, greases and organics. However, it is not commonly used as it can cause, or trigger, latex allergies. Estimates of latex sensitivity in the general population range from 0.8% to 8.2% [7]
  • NITRILE is a synthetic rubber that has better puncture and abrasion resistance than latex. It also offers better chemical protection. However, it is still not recommended for aromatic solvents, many ketones, esters, many chlorinated solvents. Some people are allergic to nitrile gloves.
  • NEOPRENE is a synthetic rubber developed as an oil resistant substitute for natural rubber. It is recommended for acids, bases, alcohols, fuels, peroxides, hydrocarbons, and phenols. It is not recommended for oxidizing acids, bases, alcohols, oils, fats, aniline, phenol, and glycol ethers.
  • BUTYL RUBBER: a flexible synthetic elastomer. It is suitable ketones, esters, and polar organic solvents. However, it is generally poor for gasoline and aliphatic, aromatic, and halogenated hydrocarbons.
  • VITON is made from a fluoro-elastomer and is a registered trademark of DuPont. It is highly chemical-resistant and has good resistance to cuts and abrasion. It is often used when working with organic solvents. However, it is expensive and is not recommended for certain ketones, esters, and amines.

Once you’ve chosen the correct glove material you need to think about thickness and how well they are made. Generally, the thicker the glove material the greater the chemical resistance. However, thick gloves can impair grip, dexterity, and safety. Picking the correct glove will depend on information from the manufacturer.

Glove quality

The production quality of all gloves is tested under the Acceptable Quality Level (AQL) regime [5]. This generates a statistical measure of the number of gloves that fail a water or compressed air leak test. An AQL of 4.0 suggests that no more than 4 in 100 gloves will fail a leak test. More common values in chemical labs are 0.65 and 1.5 which are clearly better but they certainly do not guarantee that in your box of 100 gloves there will be none with a pin hole.

Manufacturers will generally produce gloves to a much better standard than these values suggest but it is an important consideration depending on your application.

Advice to users

The following are some general observations of glove choice and do not replace consultation with a H&S expert.

  • Careful of physical abrasion: Glove robustness may be more important than chemical resistance. If the task could result in the glove ripping or create a hole this is much more of an exposure concern than molecular permeation.
  • Inspect before use: All gloves should be inspected before use for indications of degradation (swelling, cracking, shrinking, or discoloration) and any signs of cuts, splits or punctures. A damaged glove should be immediately disposed of.
  • Check the shelf life: disposable nitrile gloves for laboratory use have a shelf life of three to five years (depending on the manufacturer and the specific product). They do degrade to this should be taken seriously.
  • Double glove where appropriate: A rule of thumb is that double the thickness will quadruple the breakthrough time. As such double gloving increases protection, allows quick safe removal of a contaminated glove, and leaves residual protection. Using gloves of two different colours also makes it easier to spot holes. Double gloving for physical abrasion may also be sensible (e.g. a tough outer glove with a chemically resistant inner glove)
  • Change gloves regularly: Change gloves frequently, especially thin disposable gloves that have been exposed to hazardous chemicals. Remove gloves that may have been contaminated as soon as possible. Avoid reusing disposable gloves. Thicker reusable gloves should be rinsed after use to prolong their life and prevent the spread of chemical contamination from the dirty glove.
  • Avoid cross contamination: Remove gloves before leaving the contaminated area to prevent spread of hazard to door knobs, light switches, telephones, etc. practice removing glove without contaminating skin, clothes etc. Wash your hands thoroughly with soap (or soapless hand cleanser) and water after wearing gloves.

In the labs where I work we use the gloves set out below (see Table 2). However, this should not be seen as guidance – it is for information purposes only. Consult your H&S officer before making any decisions.

Use of gloves
Table 2: Use of gloves. Not a recommendation.

References & acknowledgments

Thank you to Dr. Jane Blunt for making me think about the gloves we use and pointing me towards some of the stories in this article.

[1] P.H. Plesch, Lose rubber gloves in science class; The Times: Letters to the Editor, 9th October, p.41 (2009)

[2] http://www.dtic.mil/dtic/tr/fulltext/u2/706360.pdf

[3] D.E. Wurster and R. Munies, Factors Influening Percutaneous Absorption II, Journal of Pharmaceutical Sciences, Vol. 54, No. 4, April 1965 p.554.

[4] K. Endicott, The Trembling Edge of Science, Dartmoth Alumni Magazine, April (1998)

[5] British Standards, BS EN 374, Protective gloves against chemicals and micro-organisms (1, 2, 3 and 4) (2003)

[6] New Mexico State University, PPE general glove guide, April 8, 2014.

[7] Grzybowski, M; Ownby, D; Rivers, E; Ander, D; Nowak, R (2002). “The prevalence of latex-specific IgE in patients presenting to an urban emergency department”. Annals of Emergency Medicine 40 (4): 411–9

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